Cardiovascular disease is the leading cause of death in the United States with over 600,000 deaths per year attributed to coronary artery disease, and over 500,000 diagnostic cardiac catheterizations performed annually in the U.S. Despite the development of multiple noninvasive tests for the detection of myocardial ischemia, up to 20% of diagnostic coronary angiograms reveal insignificant coronary artery disease. Coronary angiography, however, carries with it a high cost and low, though finite morbidity and mortality, making it inappropriate for use as a screening test. Furthermore, while it gives information regarding diameter stenoses, quantitative data regarding coronary blood flow is not generally available. We have recently developed a magnetic resonance (MR) imaging pulse sequence which permits high-resolution imaging of coronary artery blood flow in humans. Complete images may be acquired during a single breath- hold (10-15 sec) using a commercial MR scanner and surface coil. Since images can also be acquired with an effective temporal resolution of < 85 msec. Moreover, blood flow velocities within the coronary vessels can now be assessed in a non-invasive manner and without the need for any intravascular contrast agents or vascular access. Our goals include: 1. To optimize the MR methodology for imaging human coronary arteries in young adult volunteers as well as patients undergoing diagnostic cardiac catheterization in whom coronary angiography reveals normal coronary lumen; 2. To develop the means for processing the MR data into projection angiograms. The MR angiograms will be validated by comparison with conventional angiograms in patients with normal coronary artery anatomy and in those with focal stenoses; 3. To further develop the MR methodology to permit measurement of absolute coronary artery blood flow, specifically using phase-sensitive imaging in conjunction with a segmented k-space acquisition. Flow quantification techniques will be validated using flow phantoms and will be tested in patients scheduled for diagnostic coronary angiography in whom coronary artery blood flow will be assessed using either transesophageal Doppler echocardiography or intracoronary Doppler flow probes; 4. To assess changes in coronary artery blood flow following pharmacologic coronary vasodilation.